1. Field of the Invention
The present invention relates to an improved process for hydroprocessing of hydrocarbon feedstock. The process involves interbed separation of gas/liquid phases of a process stream for removal of hydrogenated impurities and gaseous hydrocarbons.
The invention relates further to a method of retrofitting or modernising an existing hydroprocessing reactor for use in the improved process.
2. Description of Related Art
Hydrocarbon feed stocks and in particular heavy hydrocarbons usually contain organic sulphur and nitrogen compounds that in a subsequent process are undesired impurities because they affect catalyst activity. These impurities must therefor be hydrogenated to hydrogen sulphide and ammonia prior to being treated in a subsequent process for further hydroprocessing of the feed stock.
A number of known processes for treatment of heavy hydrocarbon raw material fulfil different requirements concerning feed, product and cost of investment.
Thus, Verachtert et al. (U.S. Pat. No. 5,914,029) disclose a process containing a hydroprocessing reactor, cooling in several heat exchangers, gas/liquid separation and stripping of the liquid hydrocarbon.
Cash (U.S. Pat. No. 6,096,190) mentions a simple process for hydrotreatment of two different feedstocks with a common hydrogen source in one reactor. After cooling and separation, the liquid separator effluent is fed to a distillation tower.
Similarly, Kyan et al. (U.S. Pat. No. 5,603,824) send heavy distillate and light distillate to a common reactor for hydrocracking and subsequent dewaxing.
However, none of the above processes include interbed phase separation and H2S/NH3 removal and interbed product recovery by gas phase separation.
Both Chervenak et al. (U.S. Pat. No. 4,221,653) and Devenathan et al. (U.S. Pat. No. 5,624,642) disclose hydrocarbon processing including gas/liquid separation inside reactor, however, the catalyst beds involved are fluidised beds requiring recirculation of the liquid phase.
Bridge et al. U.S. Pat. No. 4,615,789 disclose a hydroprocessing reactor containing three fixed catalyst beds, downward gas/liquid flow and gas/liquid separation before the last bed. This process ensures that the liquid phase bypasses the last catalyst bed and that the gas phase process stream undergoes further hydroprocessing in absence of the liquid hydrocarbons.
In WO 97/18278 Bixel et al. describe a process for hydrocracking and dewaxing of an oil feed stock to produce lube oil. The process includes two multi-stage towers, where the process stream is cooled by quenching with hydrogen between the catalyst beds, and after first tower the gas phase of the process stream is recycled to the inlet of this first tower.
Wolk et al. disclose in U.S. Pat. No. 4,111,663 reactors with up-flow of a slurry of coal, oil and gas, where cooling between beds is performed by addition of cold hydrogen or by withdrawing process gas stream, cooling, separating, removing the liquid and returning the gas phase to the reactor between the beds.
In patent No. EP 990,693 Kalnes et al. disclose a process for producing light hydrocarbons by integrated hydrotreating and hydrocracking. In this process, the liquid phase of the effluent and the hydrogen rich gas, after further processing, are returned to the hydrocracker.
In publication DE 2,133,565 Jung et al. describe a process for hydrocracking of hydrocarbon oil, where effluent from first cracker is further processed by distillation and the heaviest fraction is further cracked before being returned to the distillation. The two hydrocracker towers are cooled by hydrogen addition between the beds.
A process for production of coke by McConaghy et al. is disclosed in SE Patent No. 8,006,852, where hydrocarbon feed is cracked in a cracker furnace before being fractionated and some of the heavier hydrocarbons from the fractionator is further hydrogenated before returning to the cracker furnace and fractionator.
In U.S. Pat. No. 3,816,296 Hass et al. describe their process for producing gasoline and midbarrel fuels from higher boiling hydrocarbons. The feed is processed by hydro-refining, cracking, separation with return of the gas phase to hydro-refining inlet and by refractionation of the liquid phase. The heaviest phase from the refractionator is treated in a second cracker, to which also nitrogen compounds are added, in order to control selectivity of the cracking process. The effluent of this second cracker is separated and the gas phase is returned to inlet of second cracker.
Many of the processes of prior art concerning hydroprocessing involve phase separation of a process stream, and the gas phase is returned to the process or recycled to the inlet of the apparatus, which the process stream just has passed through.
Prior art fails to teach separation of gas phase from liquid phase between catalyst beds inside a reactor and returning only the liquid phase with the purposes of removing H2S and NH3 and the light hydrocarbons in order to avoid excessive cracking of the light hydrocarbons and to avoid sending poisons to the subsequent catalyst beds.